The aims of this protocol are to evaluate the cause and treatment of hypokalemia in patients who maintain this problem without an obvious cause and to characterize the renal handling of sodium, potassium, magnesium and calcium in relatives of patients with genetically confirmed Gitleman's or Bartter's Syndrome. Specifically, we would like to test the hypothesis that heterozygote relatives for Gitelman's or Bartter's mutations are more susceptible diuretic-induced hypokalemia. We are also testing whether they have a lower blood pressure and/or higher bone density than their wild type relatives.